The T6373 are designed to control the valve, or the valve and the fan in 2-pipe fan-coil applications. The thermostat operates an on/off valve to provide control at the desired setpoint temperature. The fan can also be controlled from the thermostat. In some cases it is wired to run continuously, and can be switched off with the system ON/OFF switch, while with other models there is a choice of running the fan continuously, or cycling it with the thermostat. Versions are available with a manual 3-speed fan switch, and with a system on-off switch. Heat/cool changeover operation is also possible on some versions. This function can be accomplished either by a manually operated heat/ cool switch on the front of the thermostat or in some versions automatically by the use of a pipe thermostat on the supply water pipe of the fan-coil.